While few publications have documented the uptake of nanoparticles in plants, this is the first study describing uptake and distribution of the ultra-small anatase TiO 2 in the plant model system Arabidopsis. We modified the nanoparticle surface with Alizarin red S and sucrose, and demonstrated that nanoconjugates traversed cell walls, entered into plant cells, and accumulated in specific subcellular locations. Optical and X-ray fluorescence microscopy co-registered the nanoconjugates in cell vacuoles and nuclei. KeywordsAnatase TiO 2 nanoparticles; TiO 2 nanoconjugates; Arabidopsis thaliana; X-ray fluorescence microscopy (XFM)The application of nanotechnology to plant systems has lagged behind nanomedicine and nanopharmacology in spite of its potential to generate new tools for the delivery of fertilizers, herbicides and insecticides 1 , new ways to manipulate plant genomes 2 and new methods to capture and isolate plant natural products. Compared to the thousands of studies describing the uptake and trafficking of nanoparticles (NPs) in biological systems other than plants, less than twenty reports discussed NP uptake by plant species. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] These studies involved different plant species and different types of NPs which were delivered to intact plants, dissected plant organs or protoplasts using a wide range of application methods. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Despite the absence of systematic analyses, it has been determined that plants can take up NPs from the environment and transport them through the vascular system to various shoot organs. 4,9,15 However, little is known about the uptake mechanisms involved or the subcellular localization and distribution of the internalized NPs. 16 Uptake efficiency has also Figure S1), and show additional data describing NC distribution and localization in roots, hypotocyls and cotyledons (Figures S2, S3 and S4). This material is available free of charge via the Internet at http://pubs.acs.org. Here, we report on the uptake and localization of anatase titanium dioxide (TiO 2 ) NPs smaller than 5 nm in the plant model system Arabidopsis thaliana. We chose to study the Col-0 accession because this is the most commonly used ecotype within the Arabidopsis research community. 22 The numerous resources developed for this genetic background 23,24 will not only facilitate future analyses of the molecular mechanisms of uptake, intracellular localization and trafficking of NPs, but will also provide opportunities for NP-mediated manipulations of the Arabidopsis genome. In addition, the well-characterized Arabidopsis null mutants and overexpression lines for enzymes of various biochemical pathways offer the possibility for the targeted in planta chemical modification of NP surface with pathway intermediates. TiO 2 NPs with average diameters of 2.8 ± 1.4 nm and NP dispersity of 43% (see Supporting information) were synthesized by a low-temperature alkaline hydrolysis route as described previously 2...

Unsymmetric peptide bolaamphiphiles that incorporate (l-glutamyl)3glycine at one terminus and either tetraethylene glycol or aspartic acid at the other were found to form hydrogels at low wt %, presumably by self-assembling into nanofibers presenting (l-glutamyl)3glycine at their surfaces and burying the second headgroup at their cores. Transmission electron microscopy measurements on 1 wt % gels negatively stained with phosphotungstic acid and positively stained with uranyl acetate show one-dimensional objects with diameters of 5 nm and lengths in excess of 1 mum. Circular dichroism and solid-state FTIR spectra indicate the adoption of beta-sheet structure within the nanofibers.

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Exploiting the presence of undercoordinated surface Ti atoms at the tips of TiO2 nanorods and the dopamine selectivity for these Ti surface states, biotin was conjugated to TiO2 nanocrystallites using dopamine as a bridging linker. Using abiotin−avidin complex as a connector the “tip-to-tip” assembly of 400 nm elongated TiO2 rods was obtained. The photoexcitation of avidin−TiO2 hybrids resulted in the transfer of holes from nanocrystallites to protein and consequent oxidation of avidin, most probably at tyrosine 33.

The appeal of nanoscience and the allure of nanotechnology have been fostered by the promise of unique properties originating from structural features on the nanoscale. Many literature examples exist in which exceptional electronic, optical, chemical, and biological activities stem from nanoscale materials. [1][2][3][4][5][6][7] The ubiquitous attribute of these examples is their convergence from a "bottom-up" design strategy into pioneering discoveries and devices. In an effort towards the production of functional nanomaterials, we have combined the successes of nanoparticle synthesis with the selective surface reactivity of organic compounds and the self-assembly of biological molecules. Our group has previously reported on the synthesis of TiO 2 having varied physical morphologies [8][9][10] and interesting surface properties and reactivity. [11] Other investigations with TiO 2 have shown that flat surfaces reconstruct to possess lattice sites in which surface titanium atoms can adopt a non-complete coordinate character. [12,13] In addition, recent reports have suggested that particular surfaces of TiO 2 particles, such as the 001 surface, have enhanced sitespecific reaction affinities; [14][15][16] however, a specific mechanism involving the undercoordinate atomic character and enhanced surface reactivity found in TiO 2 particles has not been concluded. Here, in an effort to explain this reactivity, we describe an atomic-resolution transmission electron microscopy (TEM) investigation of surface defect sites present at the tips of high-aspect-ratio ellipsoid nanoparticles of anatase TiO 2 . We contend that the ability to chemically modify the surface of nanostructured titanium dioxide resides in specific undercoordinated "corner" defect sites that constitute the surface of high-curvature nanoparticles. By tailoring particle shape, these defect sites are spatially positioned to isolated regions of the nanoparticles. Modification of the nanorod tip surfaces with the enediol molecule dopamine resulted in relaxation of the tip defect sites to their bulklike octahedral symmetry. The reactivity of surface defect sites was used for the controlled, site-specific biotinylation of the nanorod tips. The biotinylated rods were then conjugated through a "lock and key" interaction with avidin and assembled to produce tip-connected "chainlike" structures. This approach, in addition to the abundance of titanium dioxide in a myriad of technological applications (ranging from paint fillers, to biomedical applications, to catalysis), confirms TiO 2 as a material of choice for development of inexpensive, nanoscale biocompatible devices. Determination of the chemical environment of atoms in nanoparticles, particularly at surfaces, is an exceedingly difficult challenge and has been investigated with spectroscopy techniques and microscopy such as diffuse-reflectance IR Fourier-transform spectroscopy (DRIFTS), X-ray photoelectron spectroscopy (XPS), and near-field scanning optical microscopy (NSOM). [17][18][19][20] Additionally, est...